107381domain: NAppears in sequencesa(n) = smallest composite (odd) number greater than a(n-1) such that a(n)+2n is the first prime after a(n).at n=29A189118The least semiprime (A001358) such that between it and the next n semiprimes, but not the next n+1 semiprimes, there are no primes.at n=19A228170